\startbuffer[DemoPage]
    \hfill
    \vfill    
    \midaligned{\bold{\pagenumber}}
    \vfill
    \hfill
\stopbuffer

\setupbodyfont[ss,60pt]
\setuplayout [margin=0pt, width=fit]
\setuppagenumbering [alternative=doublesided,location=]
\showframe
\setuplayout [location=middle,marking=on]


\setuppapersize[A7][A3] 
\setuparranging [2*8]

\starttext
    \dorecurse{16}{\getbuffer[DemoPage]\page}
\stoptext

